1. Field of the Invention
The invention relates to a heat exchanger for heating the water in a windshield washer system of an automotive vehicle, in which the heat exchanger makes use of the engine cooling system.
2. Background Information
Among the accessories designed to improve the ease, convenience and safety of driving an automobile, the washing of windshields by spraying water improves the action of the windshield wipers to such an extent that windshield washing systems have become standard equipment on modern vehicles. However, such systems can become completely useless at temperatures below zero degrees Celsius, because the spray nozzles tend to ice up. This lower temperature limit can be reduced by the use of an antifreeze liquid. Nevertheless, numerous inventions have proposed the heating of windshield washer fluid, thereby improving the effectiveness of the washing. Even if an antifreeze eliminates the risk of the icing of the nozzles, there is an even more serious risk, which is the instantaneous icing of the fluid sprayed on a windshield which is too cold. In such an instance, the windshield may become dangerously opaque.
Therefore, a proper heating of the washer fluid is highly desirable, between the washer fluid reservoir under the hood, where the fluid is stored, and the sprayer nozzles. An electric pump controlled by the driver is often located in the cover of the reservoir, or may be located further away, for example, on a circuit consisting of plastic tubes, e.g. industrial nylon polyamide.
The known art relating to devices for heating windshield washer fluid includes heating means employing electrical resistance, such as those described in Fed. Republic of Germany Patent No. 2,642,301 (Becker) or U.S. Pat. No. 4,575,003 (Hotshot Auto Products). The latter patent discloses heating by electrical resistance in combination with a tap from the automobile cooling circuit.
These devices have the disadvantage that they require a safety regulation to limit the heating of the resistance. Most of the other inventions, proposed in this field, use the engine cooling circuit as the heat source, which is itself regulated to a temperature which does not risk any damage if the windshield washing fluid remains at this temperature for a long time. French Patent No. 2,389,520 (Hagus C. Luchtenberg) discloses an adaptable exchanger, plated by a contact surface on, or held substantially tightly against, an existing radiator. French Patent No. 2,447,302 (Ferodo) discloses the modification of the coolant tank in the radiator. French Patent No. 2,436,045 (P. Auteroche) proposes that an exchanger be fitted to the radiator cap or even to the crankcase. These three patents, therefore, disclose additional devices which are added to the cooling circuit, and do not attempt to modify the cooling circuit as designed by the automobile designer. These additional devices are difficult to incorporate in an assembly line of a manufacturing system and do not readily lend themselves to easy installation in a manufactured automobile. Furthermore, the devices are generally incompatible with the production requirements of the automobile industry.
Other patents disclose the incorporation of an accessory in the standard coolant circulation circuit. For example, French Patent No. 2,605,273 (Valeo) discloses a spiral-shaped deformable bellows threaded around the coolant hose and French Patent No. 2,416,142 (P. Auteroche) discloses an interposed metal sleeve comprising a tubular coil. The device disclosed in French Patent No. 2,129,629 (Nitterl) performs the same function, that is, receiving heat from coolant fluid, on the reheating circuit of the carburetor. Likewise, French Patent No. 2,406,177 (Kepler) and European Patent No. 0,271,821 (Muller) disclose the incorporation of a box in the coolant circuit. Such a box is generally made of two parts assembled with a seal, and contains a tubular coil, coiled in spiral fashion around an engine coolant line where water or coolant fluid circulates, without interfering with the full cross section of the flow of the water or coolant fluid. The box in the patent to Kepler is a metal box stamped and assembled by brazing or welding, and includes an arrangement of graduated cylinders which allows for the box to be fitted to various tube diameters. The box in the patent to Muller is preferably formed of half-cylinders made of cast aluminum. The box may be bolted tight and the coil tube may be fastened by connections with O-rings and tightened in a substantially radial direction.
The devices of the known art, therefore, require additional connections of flexible hoses to rigid accessories. Such additional connections are precisely what automobile designers in general wish to avoid, given all the problems, caused by collars and other connectors. Such problems may include the ultimate removal and replacement of such collars and connectors. The cost of additional accessories, the cost of collars, the process of cutting the tubes to the correct length and any additional labor required for installation and repair of any accessories can make the overall operation generally undesirable, since the operation involves an altogether auxiliary function. At best, in such an operation, the added value of such an auxiliary function may be moderate.
Seeking reliability at low cost, the entity to which Applicant will assign this invention has obtained European Patent No. 0,243,216, which relates to a device for the tapping and/or connection of flexible lines in coolant liquid circuits or other fluids on automobile vehicles. The invention disclosed in this European patent is based on a hooping effect on the extremities of flexible coolant lines by the contraction of an external envelope of rigid polymer, which is essentially a plastic. This fitting makes it possible to connect tubes of identical or different diameters, to connect tubes of different materials, to attach taps or make "T" connections, and to install economical bleed fittings.